The present invention relates to the construction of a magnetic roll for use in a processing station of an electrostatographic printing machine.
In the well-known process of electrostatographic printing, which includes xerographic printing and copying, a charge-receptive member is initially uniformly charged, and portions of the member are discharged according to an image desired to be printed. The imagewise-discharged areas form an electrostatic latent image. This latent image is subsequently developed by applying a fine toner to the charge-receptive member, the toner adhering to those areas of the latent image which are charged in a particular way. The developed image is then transferred to a sheet, yielding a print of a desired image. Following transfer, any remaining toner on the charge-receptive member is cleaned from the charge-receptive member.
In many common designs of electrostatographic printing machines, magnetic rolls are employed in the developing station and the cleaning station. Typically, the magnetic roll includes a stationary magnet having a rotating tube or sleeve positioned concentrically thereabout. The magnetic roll defines a series of longitudinal magnetic poles arranged in alternating fashion around the circumference thereof. When the sleeve is rotated around the stationary magnetic roll, developer material (which typically includes toner and a magnetically-permeable carrier) is held by the magnetic poles to the sleeve and conveyed on the surface of the sleeve toward the charge-receptive member.
The present invention is directed toward the construction of a magnetic roll for use in an electrostatographic printer.
In the prior art, U.S. Pat. No. 4,638,281 discloses a magnetic roll which includes a central carrier, in the form of a cylinder having a set of strip-shaped cavities along longitudes thereof. Permanent magnetic components are placed in the strip-shaped cavities.
U.S. Pat. No. 4,823,102 discloses a magnetic roll having a central portion with a plurality of spaced fins extending radially therefrom. A magnet is secured in each space between adjacent fins.
U.S. Pat. No. 5,570,167 discloses a technique for molding a magnetic roll. A molten resin containing magnetic particles is injected into a mold cavity, while magnetic lines of force are applied.
U.S. Pat. No. 5,740,509 discloses a magnetic roll including a columnar magnet with a D-shaped central bore. The D-shaped bore causes one portion of the magnet to have a particularly strong magnetic pole relative to other magnetic poles along the circumference.
U.S. Pat. No. 5,894,004 discloses a mold for manufacturing a magnetic roll. The mold includes a body and an insert, which are used to provide specific configurations of magnetic poles in the finished roller.
According to one aspect of the present invention, there is provided a method of making a magnetic roll suitable for use in developing an electrostatic latent image. A first partial cylinder is provided, defining a first partial cylindrical surface. A second partial cylinder is provided, defining a second partial cylindrical surface. The first partial cylinder is attached to the second partial cylinder, thereby combining the first partial cylindrical surface with the second partial cylindrical surface. At least one magnetic pole is defined in a portion of the combined first partial cylindrical surface and second partial cylindrical surface.
According to another aspect of the present invention, there is provided a magnetic roll suitable for use in developing an electrostatic latent image. A first partial cylinder, defining a first partial cylindrical surface, is attached to a second partial cylinder, defining a second partial cylindrical surface, to yield a combined cylindrical surface. At least one magnetic pole is defined in a portion of the combined cylindrical surface.